In U.S. Pat. No. 4,025,974, issued May 31, 1977, Lea et al, there is described a self-inflating air mattress and method of making the same. In general, the air mattress comprises an airtight flexible jacket enclosing a core of a resilient, open cell, lightweight foam material. The upper and lower portions of the foam material are bonded to the envelope. The process of making this mattress comprises first making a prebonded assembly made up of two sheets of an air impermeable plastic coated fabric, with the foam core positioned between the two sheets. Heated platens are applied to this lay up, followed by applying a vacuum to the interior. The assembly is then cooled, and then moderate pressure is applied to the inside of the bonded assembly.
The mattress made according to the process described above functions quite effectively as a self-inflating air mattress, particularly adapted for use by campers or anywhere that weight and storage bulk are at a premium. The foam core is compressible, so the mattress can be rolled up into a relatively compact package. By closing the inflating valve with the mattress so rolled into a package, the mattress will remain in that rolled, compact configuration. By releasing the inflating valve, the expanding force exerted by the foam will cause the mattress to unroll to its extended use position, with the inflating air being drawn into the mattress. If desired, the mattress can be inflated by mouth and then the inflating valve is closed.
The mattress in its inflated condition provides very effective support for a person lying thereon. With the foam core being reliably bonded to the outer sheets, when a person lies on one part of the mattress so as to moderately compress the same, the other portions of the mattress tend to expand outwardly. However, the foam core, being bonded to the sheets or skin of the mattress, acts in tension to limit the movement of the two sheets away from one another, and at the same time maintains a moderate increase of air pressure within the mattress giving support to the person on the mattress. This increase in pressure resists further downward compression of the mattress under the person's weight, so that the mattress thus provides effective support. However, for such a mattress to function effectively, it must of course be air impervious. Further, the foam core must be reliably bonded to the upper and lower sheets which form the envelope.
The sheets which have been used in this process are generally made in layers. The first layer is a relatively nonstretching sheet, such as a fabric. The second layer is a thin base (or tie coat or coats) which bonds strongly to the first layer or fabric. The third layer is an intermediate coating or series of coatings of a thermoset material, or a thermoplastic material of a relatively high melting temperature. The fourth layer is a coating or series of coatings of a thermoplastic material having a melting temperature moderately below that of the intermediate coating(s). During the heating of the upper and lower sheets, the inner coating softens to some extent to permit some of the filaments of the foam core to bond to or actually penetrate into the softened fourth layer, with other filaments coming into bonding contact against the surface of the fourth layer. During the subsequent cooling step, the filaments then become securely bonded to the inner or fourth layer.
In the years during which the above process has been practiced, the formation of the sheets has been a critical factor. For reasons of material costs, and also to make the air mattress flexible and lightweight, the sheets must be made quite thin. For example, the total thickness of the sheet may be as low as 0.01 of an inch, with the two film layers each being as small as 0.001 to 0.002 of an inch in thickness. Yet, the two films of the sheet must be of sufficiently consistent quality to provide reliable bonding to the foam, and yet the total construction must be air impervious.
The common prior art method of forming the sheets used in the process noted above is to coat a fabric layer with successive layers of a liquid solution of a material such as polyurethane dissolved in a suitable solvent. A thin coat of the solution is applied to one side of the fabric, and the fabric with the thin liquid coating is then dried at a moderately elevated temperature to drive off the solvent, thus leaving a thin coating of the cured polyurethane. Then a second layer of the liquid is applied in the same manner, and subsequently heated to form an additional coating of the cured polyurethane. After several such applications of liquid followed by heating, the base coat is formed. The same procedure is used repeatedly using resins of different melting temperatures to build up the intermediate and inner layers to adequate thickness to function satisfactorily.
In the past, there have been attempts to simplify the overall mattress making process described above, and a substantial amount of this effort has been devoted to improving and simplifying the method of manufacturing the sheet used in making the air mattress. For example, instead of applying successive layers of a liquid, followed by intermediate steps of drying through the application of heat, it has been attempted simply to apply layers of solid film material against the fabric to form the two film layers of the sheet. However, in the past such attempts have been generally unsatisfactory, and it was not possible to maintain proper quality, particularly maintaining the bond strength to the first layer and the air impervious quality of the sheets.
A search of the U.S. patent literature did not reveal any patents particularly relevant to the teachings of the present invention or the problems encountered in the above described process. However, the patents noted in that search are recited herein as background information relating to films and adhesives in general.
U.S. Pat. No. 3,623,943, Feldmellen et al, shows a composite plate where there are outer metal sheets with a core made from a polyolefin layer. The metal is bonded to the core through an adhesive having a relatively low melting point, and between the adhesive and the polyolefin core, there is an intermediate layer of polyethylene having a relatively higher melting point.
U.S. Pat. No. 3,666,615, Toshiharu et al, discloses a layered sheet material to be used as electrical insulation. There is a thermosetting resin layer and a hardening agent layer, these two layers being separated by a contact-preventive film layer which melts on heating and allows the thermosetting resin layer and the hardening layer to react.
U.S. Pat. No. 4,056,422, Staats, illustrates a two-stage process for laminating a polyester-polyethylene film to a substrate, such as a photograph. The substrate with the film being applied thereto is passed through a lower temperature set of rolls and then through a higher temperature set of rolls. The patent states that this eliminates an undesired "blush" that would otherwise interfere with the aesthetics of the underlying member (e.g. a photograph), and yet prevents the formation of bubbles. U.S. Pat. No. 4,273,827, Sweeney et al, discloses an adhesive assembly having first and second adhesives with a barrier separating the two adhesives.
It is an object of the present invention to provide an improved overall method for making an inflating member, such as the self-inflating air mattress described above, and particularly to provide an improved method of forming the sheets used in that overall process. The instant process is less expensive, with the sheets being tougher and more air impervious because they are made a solid polymer film instead of solvent applied layers of resin. This also makes the system more tolerant to physical flaws in the fabric. It is a further object to provide an inflatable member, such as the air mattress noted above, made from such process.